Undercover
by Liv Wilder
Summary: AU set early Season 4. "Where's Beckett?" A dark head appears over the top of a computer screen. "Yo! Can't say, bro." Esposito taps the side of his nose. "Top Secret." "Yeah, need to know," Ryan chips in, grinning at the immediate look of frustration and indignation that pops up on Castle's face when Kevin backs up his partner, refusing to help. COMPLETE


_A/N: I saw this photo on Instagram and well...would be rude not to. AU set early season 4. Credit for the photo goes to Michael Kors._

* * *

 _Undercover_

It's mid-morning by the time Castle swaggers into the precinct with a tray of coffees and a bag of pastries. Grease stains the paper sack like guilt. He comes to a stop at Beckett's desk, dumps his loot, sheds his jacket to his chair scoping out the homicide floor all the while. Once he's installed, he checks his partner's computer screen, which is dark, and then he feels the back of the monitor. No heat means the computer has been switched off overnight, which means that Beckett isn't in yet. He doesn't recall her telling him about any early appointment - no doctor or dentist or therapy session - and he hasn't been notified of a case so…

He turns to address the boys, jabbing his thumb at the empty desk. "Where's Beckett?"

A dark head appears over the top of a computer screen. "Yo! Can't say, bro." Esposito taps the side of his nose. "Top Secret."

"Yeah, need to know," Ryan chips in, grinning at the immediate look of frustration and indignation that pops up on Castle's face when Kevin backs up his partner, refusing to help.

The writer decides to ignore Ryan for now and stay with Esposito until the well runs dry.

" _Can't_ say as in _won't_ say or…" He lets the question float on a raft of silence hoping that one of the two detectives might crack and let something slip. They usually do. When nothing is forthcoming, he casually pulls a set of keys from his pocket and dangles them from the tip of one meaty finger, loudly clearing his throat to draw their attention.

Ryan cracks first, lunges and snatches the Ferrari keychain from the writer's hand while blurting, "Undercover. She's working undercover."

Castle's eyes swell to twice their normal size. "Undercover where? _Alone?_ " He looks from one to the other, not hiding the accompanying flash of accusation that they would abandon her.

"More like surveillance," Esposito corrects, giving Kevin a glare of deep disappointment. He adds a tut and a shake of his head for good measure.

Castle soaks it all up.

"What's she…uh…what's she surveilling?" He tries to ask this as nonchalantly as possible, which isn't very given he's like a cat on a hot tin roof by now, needing, needing to know with the very core of his nosy, inquisitive, writerly being where his partner is and what's she's up to, with whom, and why no one (especially Beckett) asked him to come along.

"Biker gang."

Ryan is the one to offer this tasty tidbit of information, and Esposito smacks him on the arm, thus commencing a pantomime of pushing and shoving that a child could see is just for laughs. Only Castle is blinded by something else.

" _What?_ " Castle shrieks like a girl. "By _herself?_ "

The two detectives nod.

"She's a big girl," Espo reminds him.

"Just don't let her hear you say that," Ryan sniggers.

"Why'd no one tell me? I'm her partner. I'm— _A biker gang?_ "

Esposito jabs his chin in Castle's direction. "Look at chu, bro. Ain't no way you're blending in." He purses his lips and shakes his head. "No way, man."

"I beg your—"

When Castle turns to Ryan for affirmation the younger cop shakes his head. He looks kind of embarrassed. "Beckett's instructions were very specific."

" _Very specific_ ," they gravely repeat.

Castle looks panic stricken and gutted. "She's…she really said that? I can't go undercover with her because I wouldn't… _blend in?_ "

The boys nod again and at least this time they both look a little sorry for him.

"Look, we can tell you where she is, man. But you know…didn't come from us," Esposito offers, jabbing his thumb towards each of them before making Castle promise. Ryan nods along like a bobble head doll.

"Sure. Yeah. Of course. And I can _totally_ fit in. I can disappear. Guys, I am a _master_ of _disguise_ ," he pridefully assures them. "You believe me, right? I am a _ghost_."

There's an uncomfortable pause before Esposito gives him a hard stare and says, "Yeah, okay. Sure you are. Just…don't lose your cool, jefe."

Castle can't take a hint and tries to pile on the persuasion. "Come on, guys. _Halloween._ Who's the master? Every year? My own mother wouldn't recognize me if I didn't want her to."

Ryan and Esposito exchange a look that Castle decides is best not deciphered or responded to if he wants to find out where Beckett has gone.

* * *

A stiff breeze eddies off Columbus and runs along West 84th. The asphalt throws up whirlwinds of grit and small pieces of trash that pirouette like dust devils in the northeast corner of the yard.

Beckett closes the gate behind her and heads for her Harley, which is parked over by the chain link fence. She's smiling to herself as she walks because today is a good day. Today is a great example of why she got into policing in the first place. Or rather it's the reason _most_ people get into police work – to make a difference, to do some good in their town, to help strengthen the community and to keep people safe.

Kids are filing back into class as she sets down her helmet, throws her leg over the saddle and sits astride her bike. While she gets settled, she watches the janitor and a teaching assistant gather up cones and markers from across the schoolyard. A group of 3rd Graders give her a big wave, little girls dancing in line, chattering and giggling as they move like an unruly crocodile back towards the building. Kate raises her camera and snaps a shot for posterity. Good memories, she thinks, before her attention is snagged by the growl of a familiar-sounding engine somewhere over to her right.

And out of the corner of her vision, a hot streak of red.

* * *

Castle's rear fender just clears a fire hydrant and no more, but he'll risk it because he's just spotted Beckett, _on her motorbike_ , and this is the only spot that's open on the entire block. He shuts off the engine as quickly as he can when he observes the stiffening of his partner's shoulders in response to the guttural throb of his Ferrari. She's so astute, always acutely aware of her surroundings, particularly when working undercover, so of course she wouldn't miss his arrival. He just hopes she's not too mad that he got the boys to cough up her location when she clearly didn't intend for him to be here today.

More than anything, he wants her to see him as an asset, in all areas of her life. Things have been good between them, better he hopes after their talk on the swings. But he's taking it really slowly, and he doesn't want to put a foot wrong and risk her shutting him out again. For that reason, turning up uninvited to crash her stakeout is supremely risky. But she's his partner. What else is he going to do?

 _And_ _she's on her motorbike._ So where the hell else would he be, he thinks, gawping from the interior of the car at her long legs spread either side of the Harley. Her dark jeans are like a second skin as they cling to her thighs and the firm curve of her butt. She's wearing a short, brown leather biker jacket he's never seen before. Gold buttons the size of dimes decorate the cuffs and front of the waist-skimming coat, which is more Michael Kors than the worn vests pockmarked with club patches you'd typically see on the backs of most outlaw motorcycle gangs. But this red flag is lost on Castle. He's more fixated on the way Beckett's hair shines like polished chestnuts in the sunlight as he sighs like the lovesick man he is. She's gorgeous. What were the guys thinking, letting her scope out a biker gang by herself?

He slams the car door a little too loud, flinches and then squares his shoulders, preparing to do battle against any trouble that comes his way – whether from his partner or from some hard nut, crazed "One Percenters."

"Beckett! Hey, Beckett," he calls, locking the car and jogging towards her.

* * *

Castle approaches with more swagger than usual. It throws Kate for a second, this act he's putting on. Also, he's dressed differently. Gone is the dark, conservative button down and sports coat. Instead, he's wearing a plain white t-shirt, jeans and a black leather biker jacket with the collar turned up. His hair looks kind of finger-tousled, as if he's tried to work more body and pomp into it than usual. It falls short of a full on pompadour but it comes pretty close.

"Castle, what the hell?" she hisses, and he slows from a cowboy swagger to a furtive crawl.

"Too much?" he asks as he nears her, almost mouthing the words instead of speaking them. "How's the UC detail going? Who's our target?" he asks out one side of his mouth, glancing around with more theatrics than actual subtlety. Belatedly, he wonders what outlaw gang would ever hang out near a K-5.

Beckett frowns. "UC? Who's our target? Castle, what are you talking about?"

"Look, I know it's top secret and you didn't want me here because you didn't think I could blend in, but…" He holds out a hand and kind of runs it up and down his own body. He's like a woman emerging from a department store dressing room with a new outfit to show off, all ' _tah dah and how do I look?'_

Kate bites the inside of her cheek and fights a bubble of laughter as realization dawns. "Castle, this is a Community Policing gig. I'm teaching bike safety to little kids." She squints as she takes him in. "Why are you dressed like _James Dean_?"

Castle splutters. "But…but the guys said you were undercover. Surveilling a biker…gang they said— I'll kill them."

Kate bites her cheek, watching it hit him how he's been had. "And yet you brought a _Ferrari_ to a stakeout?"

She doesn't think she's ever seen his face look redder. It almost matches the color of his car. But his embarrassment and loss of suave is kind of endearing, however. "I think you've been duped," she tells him, reaching out to tug on his collar, the gesture affectionate and familiar. "Hope it didn't cost you."

Castle looks so dopey. But now he knows she's not mad at him he doesn't care about the boys and their game. "Nah. I dangled my keys in front of Ryan, but it was just a torch on a Ferrari keychain. He fell for it though. Spilled the beans."

Kate laughs and when Castle smiles back she can't help praising him for his cunning. "Smart. Really smart move, Rick."

He scuffs the ground with the toe of his chunky black shoe, suddenly bashful and also grateful she doesn't seem to want to make a big deal out of him letting himself get scammed by the guys. "I'm sorry I crashed your community thing, Beckett."

When she reaches out and squeezes his arm he looks first at her fingers resting on his jacket and then up at her face to gauge her mood. "Hey. It's fine," she tells him gently. "I'm actually done for the day."

He looks around, watching the last of the 3rd Grade stragglers run inside. "Why here?" he asks out of genuine curiosity.

"The Sarah Anderson School?" Kate smiles. "This was my first school. I attended PS9 from Kindergarten through 2nd Grade, and then my parents could afford to send me to private school." She shrugs and turns to look at the empty schoolyard along with her partner. "So I like coming back here when I can."

"Happy memories?"

"Yeah. Pretty happy. For the little geek I was back then."

Castle laughs. "I would love to have seen you running around that yard in a plaid kilt and a little—"

Kate reaches out and touches the tips of her fingers to his lips. Castle is shocked at first and then insanely tempted to take her fingers into his mouth and suck on them. She removes them before he can act out that particular fantasy.

"Hold that thought before this gets any creepier," she warns him.

Castle looks affronted. "I meant if I was a little kid too," he insists.

"Yeah. Sure."

"Beckett, I'm not like that. You know me," the writer protests, oblivious to her teasing tone and the glint of mischief in her eye.

God he's easy today.

She prods him in the shoulder. "You still pull my pigtails. Even now," she tells him, offering up a warm and intimate smile. It's a little piece of their shared history, and they both know how much it means to get from there to here, with everything they've been through, and still be on track for something bigger.

Castle looks delighted. "I do. Don't I? And you pull mine, too, Beckett."

They smile at one another for a long, tender moment, a moment that is just for the two of them; that connection they share stronger than ever. They are two lonely souls who've managed to find one another in a world full of people. Some days - special days like this - it feels like nothing less than a miracle.

Kate reaches into the box pannier behind her, on the side of the bike, and produces a spare helmet. Castle watches her turn back towards him, his jaw slowly dropping when he realizes what's going on. She hands the helmet to him. "Might ruin your hairdo. But I'll make the ride worth your while," she winks, laughing when he draws a sharp, gasping breath of surprise at the note of suggestion in her voice.

"You…you're letting me ride with you?"

Kate smiles and nods. "You up for that?" she challenges Castle.

Hurriedly, in case she changes her mind, he squeezes the helmet over his head and begins fastening the chinstrap. He has dreamed of this moment so many times. But still the thought of actually climbing aboard her Harley-Davidson, sitting behind her and wrapping his arms around her body sends blood rushing from his brain to other parts of his anatomy. He just hopes he can get his leg over, so to speak, before his partner notices that he's…compromised.

"This okay?" Castle asks, once she's released the kickstand and he's seated astride the bike behind Kate.

"Great. Just lean with the bike and hold onto me," she tells him as she fires up the engine.

Beneath them, the throb of the twin cam sends sparks shooting up and down Castle's already highly-sensitized spine. He squeezes his eyes closed for a second and breathes deeply through his nose.

"You okay back there?" Kate checks once more when she fails to feel Castle's hands on her.

He gives her a thumbs up signal over the noise of the bike. So Kate reaches back and grabs one of his hands, placing it on her stomach so that he gets the idea.

"Better?" Castle asks, his chin almost on her shoulder so that he can make himself heard. He feels something heavy dislodge from his chest the second his arms are firmly wrapped around his partner, like this is how they're supposed to be.

He watches Kate nod her head and then she raises her voice to yell at him.

"Wanna go grab a beer? I know this great biker bar in the East Village, _Otto's Shrunken Head._ You'll fit right in."

Castle's laughter booms between them and he can feel Kate's body shake with it inside the circle of his arms. He makes a mental note to thank the boys for their prank this morning because this has turned out to be a very good day. Oh, it's a very good day indeed.

 _The End_

* * *

 _Thank you for reading. The second chapter of "Always A Bridesmaid" is in final edit and will be along soon, if you're reading that one, too. This just kind of inserted itself and with funny stories I find you have to get them down right away. Cheers, guys._


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